Characteristics of the eye in combination with eyewear such as, distance between the left and right eye pupils known as pupillary distance (PD); frame wraps around the face of its wearer at the wrap angle, draw a line through the 2 edges of left rim and draw another line for right rim, the lesser of the two angles between these two lines is known as the wrap angle (WA); distance between center of pupil and bottom of the lens known as segment height (SH); angle between vertical and the plane of the lens known as the pantoscopic tilt or angle (PA); and distance between pupil and back side of the lens know as vertex distance (VD), are critical pieces of information for designing eyewear for patients wearing eyeglass. Traditional ways use rulers or protractors to manually carry out such measurements. Automatic methods may use a digital camera to capture patient faces and a computerized system to calculate eye characteristics based on the capture images. The computerized system needs a scale factor to convert information extracted from the captured image into the actual distance and/or angles.
Prior art, U.S. Pat. No. 6,535,223B1, titled “METHOD AND SYSTEM FOR DETERMINING PUPILTARY DISTANT AND ELEMENT HEIGHT” uses a monetary coin of known dimensions held on chin as the reference object to scale the distances measured within points in the captured image. This is not something easy to use and patients getting their measurements taken do not enjoy the experience. Further there is no correction for the errors introduced in the reference coin part of the image due to tilt and yaw. Reference error translates to a bigger error in the measurement.
Prior art, U.S. Pat. No. 5,592,248 titled “COMPUTERIZED METHOD FOR FITTING EYEGLASSES” uses a camera on trips and patients chin fixed on a fixture at fixed distance to know the distance from the camera to the chin as reference. The deficiency is that the temple of the patient can move back and forward a few mm's from the chin distance introducing errors in the reference distance. The camera on tripod may have yaw error if not carefully inspected any time. The tilt or yaw error due to face tilt and yaw also introduces errors in the measurement. Reference error translates to a bigger error in the measurement.
Prior art, patent publication N0:US2013/0278895A1 describes using a pair of laser to draw reference objects on the face of the patient to get reference measurement. The laser system needs individual calibration or there will be errors in the reference objects due to manufacturing variations.
Contemporary measurement systems still use reference scales or devices with known information to obtain the scale factors. The reference devices may be worn by the patients and are visible on the captured image. Some systems are able to generate reference points with the known distance of the patient's face to replace the reference devices. Such measurement methods create distractions or unintended errors if the patient face is not correctly positioned and aligned with the measurement devices. The users are requested to train or ask the patient to obey instruction step by step.
Developing a quick and reference object free measurement method to extract eye characteristics is a crucial task. The invention aims to remove the need of reference devices or scales while keeping measurements valid with minimum errors. The reference object free measurement technique decreases measurement time, reduces the responsibilities of the users, and guarantees less stress for the patient during measurement.